WELLINGTON - New Zealand is looking to return to operation one of its idled offshore patrol vessels after a specialist dive ship sank this month, a defense spokesperson said on Thursday.

The Manawanui, a specialist hydrographic ship, left the navy with just five operational ships after sinking on a reef it was surveying off the coast of Samoa, since three had been put into "care and custody" because of staff shortages.

The defense force and its partners were gauging how much work would be needed to bring an offshore patrol vessel back into operation, the spokesperson told Reuters.

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"That assessment work will be complete by the end of the month and will determine the time frame for subsequent regeneration," the spokesperson said in an email.

The capability challenges facing the New Zealand Defence Forces returned to the spotlight when it flagged constraints last October on its ability to tackle humanitarian emergencies in the Pacific during the cyclone season.

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New Zealand's military stands ready to respond to any natural disasters in the region, the spokesperson added.